State monitoring apparatuses (so-called driver monitoring systems) have been conventionally known which are mounted in vehicles and monitor the state of the occupants of the vehicles for the purpose of ensuring safe driving of the vehicles (Refer to Patent Literature 1, for example).
This type of state monitoring apparatus includes: an image pickup system that generates a picture image; and a state monitoring portion that monitors the state of the occupant of the host vehicle based on the result obtained by processing the picture image generated at the image pickup system. The image pickup system includes: at least one floodlight projector that emits light (hereafter, referred to as illumination light) of a wavelength including at least near infrared; and a camera that forms an image from the light, which is reflected from the area irradiated with the illumination light by the floodlight projector and incident on a camera lens, using an image sensor having a plurality of pixels and thereby generates a picture image.
The camera used in the image pickup system is installed in an appropriate position together with a lens having such an angle of view providing an image pickup area where the face of an occupant is probably positioned, in consideration of changes in the posture of an occupant of average somatotype sitting on a seat of the host vehicle in ordinary motion during driving. Such an occupant of average somatotype is, for example, of eyellipse 99 percentile defined in “ISO4513 Road vehicles-Visibility-Method for establishment of eyellipses for driver's eye location” or “JIS D 0021 Eye Range of Drivers for Automobiles”. Stably monitoring the state of occupants using such a camera requires acquiring continuously picture images of the brightness and contrast suitable for image processing in a state monitoring portion from the image pickup area, by projecting as uniformly as possible the illumination light having a predetermined intensity reference value or higher to an object to be imaged. Eyellipse is the abbreviation of eye and ellipse and is used to plot the statistical distribution of the positions of eyes.